JPH0727527Y2 - Shielded wire - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a shielded wire having a good space factor, a low capacitance, and an excellent withstand voltage characteristic.

"Prior art" Conventionally, shielded wires using expanded polyethylene as the insulating layer of the inner conductor are used for signal transmission between television antenna and tuner, video signal transmission, computer equipment connection, etc. Widely used as electric wire.

In the above applications, the signal to be transmitted is a high-frequency current with a normal frequency of 1 MHz or more, and the voltage value may be weak, so in order to avoid the influence of electromagnetic field noise around it, use a shield structure with an external conductor. Often.

However, since the electric wire having the shielding structure has a structure in which an insulator is interposed between the inner conductor and the outer conductor, it is unavoidable that a capacitance is generated between the inner conductor and the outer conductor because of the structure.

The electrostatic capacitance between the inner conductor and the outer conductor becomes a problem especially when transmitting a high frequency current, and there is a problem that the strength of a transmission signal is attenuated when the transmission distance becomes long.

To solve this problem, the dielectric constant (relative permittivity) of the insulator between the inner conductor and the outer conductor may be lowered, which lowers the dielectric constant and the electrostatic capacitance between the inner conductor and the outer conductor. Various methods have been studied. For example, in the case of expanded polyethylene, the dielectric constant can be arbitrarily controlled by changing the porosity (total volume of bubbles existing in the material / volume of the entire material). It is a material suitable as an insulating material and is widely used in practice.

For example, the dielectric constant (relative permittivity) of unfoamed polyethylene
Is about 2.2 to 2.3, but the porosity can be lowered to about 1.3 to 1.5 by setting the porosity to 50%.

However, in recent years, particularly in applications such as computer-to-device connection, it is often necessary to transmit many types of signals at the same time, and there is a limit to the electrical multiplexing of transmission signals. It is often necessary to transmit many types of signals simultaneously in parallel.

In such a case, naturally, 100 or more electric wires for signal transmission are also required, so it is desirable that one electric wire has a diameter as small as possible from the viewpoint of the space factor.

However, the shielded electric wires using foamed polyethylene as an insulating layer, which have been known so far, often have a thickness of foamed polyethylene layer of usually 300 microns (0.3 mm) or more, and those of 300 microns or less are not known.

In this case, for example, if the diameter of the inner conductor is 200 microns, the diameter of only the inner conductor and the insulating layer is 800 microns (0.8mm).
Therefore, if an outer conductor and an insulating sheath are provided, normally only a diameter of 1.0 mm or more can be obtained.

Even if the conductor diameter is halved to 100 microns, the inner conductor and insulating layer will be 700 microns, which is not very effective in improving the space factor.

If the thickness of the insulation layer of the inner conductor is set to half, which is 150 microns, the diameter of the inner conductor and the insulation layer will be 500 microns even if the conductor has a thickness of 200 microns. It is effective in improving the factor.

Furthermore, it goes without saying that if the thickness of the insulating layer is set to 100 microns or less, the internal conductor and the insulating layer can be 400 microns or less in diameter even if the conductor diameter is 200 microns. It can be understood that thinning is extremely effective in improving the space factor.

However, when the thickness of the insulating layer, particularly the foamed polyethylene insulating layer, is reduced, there arise problems such as a decrease in withstand voltage and a defect such as a pinhole which is likely to be caused by an external impact.

For example, when measuring the DC withstand voltage of an electric wire with an insulating layer of a foamed low-density polyethylene layer with a conductor diameter of 200 microns and a wall thickness of 300 microns (foamed bubble diameter is controlled to be less than 300 microns), a withstand voltage of approximately 3.4kV at room temperature While it has voltage characteristics,
Foamed low-density polyethylene layer with conductor diameter of 200 microns and wall thickness of 100 microns (foamed bubble diameter controlled to less than 100 microns,
The type of low-density polyethylene is the same as the above-mentioned one having a thickness of 300 microns). When the DC withstand voltage of an electric wire having an insulating layer is measured, only a withstand voltage characteristic of about 0.43 kV can be obtained at room temperature.

"Problems to be solved by the invention" As described above, shielded wires having expanded polyethylene as an insulating layer are widely used as wires for connecting devices such as computers. As for the electric wire to be used, it is not known that the thickness of the insulating layer is 300 μm or less, which is not preferable in terms of space factor. On the other hand, when the thickness of the foamed polyethylene insulating layer is made thin, it is very effective in improving the space factor, but on the other hand, the withstand voltage characteristic is deteriorated, which causes new problems in practical use.

Therefore, there is a demand for the development of a shielded electric wire of a foamed polyethylene electric wire which has no problem such as a decrease in withstand voltage and has a thin insulating layer.

"Means for Solving the Problem" That is, the shielded electric wire of the present invention is as shown in FIG.
The insulating layer (2) of the inner conductor (1) is foamed polyethylene, the thickness of the foamed polyethylene layer is 100 μm or less, and the maximum diameter of the closed cells of the foamed polyethylene layer is 1/2 or less of the wall thickness. It is characterized by being. In FIG. 1, (3) is an outer conductor and (4) is an insulating sheath.

The present invention will be described in detail below.

The inventors of the present invention have made extensive studies on the above problems, and as a result,
Even if the thickness of the foamed polyethylene insulation layer is 100 microns or less, if the diameter of the foamed bubbles in the insulation layer is controlled to 1/2 or less of the wall thickness, the insulation layer will not be significantly reduced in voltage resistance. The inventors have found that it is possible to reduce the dielectric constant, and have completed the present invention based on such findings.

For example, a foamed low-density polyethylene with a conductor diameter of 200 microns and an insulating layer with a maximum bubble diameter of 30 microns controlled to a thickness of 90 microns (density of low-density polyethylene: 0.919g / cm
³ , the DC withstand voltage of the wire formed with a melting point of 107 ° C) was measured, and a withstand voltage characteristic of about 2.0 kV was obtained at room temperature.

The diameter of the foam bubbles present in the polyethylene foam layer, which is the insulating layer, is greatly related to the DC withstand voltage of the wire.There is a tendency for the DC withstand voltage of the wire to improve as the diameter of the foam bubbles present in the polyethylene foam layer decreases. Especially, when the maximum value of the foamed cell diameter was set to 1/2 or less of the wall thickness, the phenomenon that the withstand voltage was rapidly improved was observed.

[Examples] Examples of the present invention will be described below.

Example 1. A tin-plated single wire with an outer diameter of 200 μm (tin-plated thickness of about 10 μm) is used as an inner conductor, and a foamed low-density polyethylene layer with a wall thickness of 80 μm (the density of low-density polyethylene is used around it). 0.920g / cm ³ , melting point 112 ℃, bubble diameter in foamed low density polyethylene is controlled up to 30 microns)
An outer conductor covered with a tin-plated conductor with an outer diameter of 50 microns, and a low-density polyethylene with a wall thickness of 100 microns (a density of low-density polyethylene of 0.923 g / cm ³ , a melting point of 106 ° C). ) A shielded electric wire provided with a sheath was obtained.

As a result of measuring the electrostatic capacitance between the inner conductor and the outer conductor of this shielded wire, the average was 96 pF / m (1 KHz, 25 ° C).

The DC withstand voltage of this shielded wire (a positive electrode connected to the inner conductor and a negative electrode connected to the outer conductor) was measured, and an average value of 2.2 kV was obtained.

Hereinafter, Examples 1 to 7 are shown in Table 1, and Comparative Examples 1 to 7 are shown in Table 2. The tin thickness of the ta conductor used in the table is about 10
It is of the micron type. Moreover, Examples 2 to 7 and Comparative Example 1
The capacitance and the DC withstand voltage of the shielded wires of Nos. 7 to 7 are the same as in Example 1 and are low-density polyethylene having a thickness of 100 microns (density of low-density polyethylene 0.923 g / cm ³ , melting point 106 ° C.)
It is the measurement value of the structure provided with the sheath of.

[Advantage of the Invention] As described above, according to the present invention, a shielded wire having a small capacitance between the inner conductor and the outer conductor and excellent withstand voltage characteristics and a good space factor can be obtained. There are some electric wires that have a very high utility value as wires for inter-connection.

[Brief description of drawings]

FIG. 1 shows an example of the cross-sectional structure of the shielded electric wire of the present invention. (1) is an inner conductor, (2) is a wall thickness of 100.
A foamed polyethylene layer having a micron diameter or less and a maximum bubble diameter controlled to ½ or less of the wall thickness, (3) an outer conductor, and (4) an insulating sheath.

Claims (1)

[Scope of utility model registration request] 1. The insulating layer of the inner conductor is foamed polyethylene, the thickness of the foamed polyethylene layer is 100 μm or less, and the maximum diameter of the closed cells of the foamed polyethylene layer is 1/2 or less of the wall thickness. There is a shielded electric wire.